Semiconductor detectors with butt-end coupled waveguide and method of forming the same

ABSTRACT

The present disclosure generally relates to semiconductor detectors for use in optoelectronic/photonic devices and integrated circuit (IC) chips, and methods for forming same. The present disclosure also relates to photodetectors integrated with waveguide stacks, more particularly, photodetectors with butt-end coupled waveguides. The present disclosure also relates to methods of forming such structures.

FIELD OF THE INVENTION

The present disclosure generally relates to semiconductor detectors foruse in optoelectronic/photonic devices and integrated circuit (IC)chips, and methods for forming same. The present disclosure also relatesto photodetectors integrated with waveguide stacks, more particularly,photodetectors with butt-end coupled waveguides. The present disclosurealso relates to methods of forming such structures.

BACKGROUND

Semiconductor detectors, such as photodetectors, are sensors that detectlight or other electromagnetic energy and may typically be found inoptoelectronic or photonic devices that are manufactured usingsemiconductor processes. The use of such devices in high-speed switchingand transceiver devices in data communications are but a few examplesthat highlight the advantages of processing both optical and electricalsignals within a single integrated circuit (IC) device.

An integrated photonic device may include both photodetector andwaveguide (e.g., an optical waveguide) fabricated on a single substrate.The waveguide serves as a channel to guide electromagnetic waves intothe photodetector by confining the waves to propagate in one dimensionin order to minimize loss of energy or power. Ideally, it is desirableto have the waveguide and photodetector sections achieve a couplingefficiency for the electromagnetic waves as close as possible to 100percent for both transverse-electric (TE) and transverse-magnetic (TM)polarized modes. However, in practice, the coupling efficiency betweenthe waveguide and photodetector sections is lower due to mismatches inthe mode profiles and mode indices during optical transmission ofelectromagnetic waves, which limits the performance of photodetector(e.g., loss of energy/power in the photodetector).

Therefore, there is a need to provide semiconductor devices and methodsof forming the same that can overcome, or at least ameliorate, one ormore of the disadvantages as described above.

SUMMARY

In an aspect of the present disclosure, there is provided asemiconductor device having a substrate, a semiconductor layer having awaveguide section and an adjoining active section above the substrate, asemiconductor detector disposed on the active section of thesemiconductor layer, a dielectric layer disposed over the semiconductordetector, and a waveguide structure above the waveguide section of thesemiconductor layer and adjacent to the semiconductor detector.

In another aspect of the present disclosure, there is provided asemiconductor device having a substrate, a semiconductor layer having awaveguide section and an adjoining active section above the substrate, asemiconductor detector disposed on the active section of thesemiconductor layer, a dielectric layer disposed over the semiconductordetector and a plurality of waveguide structures that are verticallystacked above the waveguide section of the semiconductor layer andadjacent to the semiconductor detector.

In yet another aspect of the present disclosure, there is provided amethod of forming a semiconductor device by providing a semiconductorlayer above a substrate, patterning the semiconductor layer to form awaveguide section and an adjoining active section, forming asemiconductor detector on the active section, forming a dielectric layerover and covering the semiconductor detector, and forming a waveguidestructure above the waveguide section of the semiconductor layer, wherethe waveguide structure is formed adjacent to the semiconductordetector.

Advantageously, the present disclosure is found to provide a highermodal effective index of the device and an improved effective indexmatch between the waveguides and the semiconductor detector.Additionally, the configuration of the present structure is found toprovide an increased modal overlap and therefore achieving significantlyenhanced coupling efficiency between the waveguides and thesemiconductor detector for electromagnetic waves transmitting in both TEand TM modes.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be understood by reference to the followingdescription taken in conjunction with the accompanying drawings.

For simplicity and clarity of illustration, the drawings illustrate thegeneral manner of construction, and certain descriptions and details ofwell-known features and techniques may be omitted to avoid unnecessarilyobscuring the discussion of the described embodiments of the presentdisclosure. Additionally, elements in the drawings are not necessarilydrawn to scale. For example, the dimensions of some of the elements inthe drawings may be exaggerated relative to other elements to helpimprove understanding of embodiments of the present disclosure. The samereference numerals in different drawings denote the same elements, whilesimilar reference numerals may, but do not necessarily, denote similarelements.

FIGS. 1A to 1F are cross-sectional views of exemplary semiconductordevices having a waveguide structure and a semiconductor detector, inaccordance with embodiments of the present disclosure.

FIGS. 2A, 2A′, 2B, and 2B′ are cross-sectional views of exemplarysemiconductor devices having vertically stacked waveguide structures anda semiconductor detector, in accordance with embodiments of the presentdisclosure.

FIGS. 3A to 3E are plan views of the various exemplary layouts of thewaveguide structure represented by FIG. 1A and the semiconductordetector, in accordance with the present disclosure. Line X-X′ in FIGS.3A to 3E indicates the section line for the cross-sectional view in FIG.1A.

FIGS. 4A to 4D are plan views of the various exemplary layouts of thevertically stacked waveguide structures represented by FIG. 2A and thesemiconductor detector, in accordance with the present disclosure. LineX-X′ in FIGS. 4A to 4D indicates the section line for thecross-sectional view in FIG. 2A′.

FIGS. 5A to 5G are cross-sectional views and illustrate an example ofvarious processing stages for forming a semiconductor device, inaccordance with embodiments of the present disclosure.

FIGS. 5D′ to 5G′ are cross-sectional views and illustrate anotherexample of various processing stages for forming a semiconductor device,in accordance with embodiments of the present disclosure. FIG. 5D′continues from the embodiment shown in FIG. 5C.

FIG. 6 is a cross-sectional view illustrating a semiconductorcomparative test device without a waveguide structure.

DETAILED DESCRIPTION

Various illustrative embodiments of the present disclosure are describedbelow. The embodiments disclosed herein are exemplary and not intendedto be exhaustive or limiting to the present disclosure.

FIGS. 1A to 1F depict exemplary semiconductor devices in accordance withembodiments of the present disclosure. As shown, the semiconductordevices include a substrate 102, and a semiconductor layer 106 disposedabove the substrate 102. A buried insulator layer 104 (e.g., an oxidelayer) may be disposed in between the semiconductor layer 106 and thesubstrate 102. The semiconductor layer 106 has a waveguide section 110and an adjoining active section 108. A semiconductor detector 126 isdisposed on the active section 108 of the semiconductor layer 106 and awaveguide structure 122 is disposed above the waveguide section 110 ofthe semiconductor layer 106. A dielectric layer 114 is disposed over thesemiconductor detector 126. The embodiment shown in FIG. 1A may bepreferred to the embodiments shown in FIGS. 1B to 1F.

The substrate 102 may be made of any semiconductor material, such assilicon, germanium, silicon germanium (SiGe), silicon carbide, and thoseconsisting essentially of III-V compound semiconductors, such as GaAs,II-VI compound semiconductors such as ZnSe.

The substrate 102 may be a semiconductor-on-insulator substrate or abulk semiconductor substrate. Examples of a semiconductor-on-insulatorsubstrate may include, but not limited to, an organic semiconductor or alayered semiconductor, such as Si/SiGe, a silicon-on-insulator (SOI), agermanium-on-insulator (GOI), or a SiGe-on-insulator. A portion or theentire semiconductor substrate 102 may be amorphous, polycrystalline, ormonocrystalline.

The semiconductor layer 106 may be made of any semiconductor material,such as silicon, germanium, silicon germanium (SiGe), silicon carbide,and those consisting essentially of III-V compound semiconductors, suchas GaAs, II-VI compound semiconductors such as ZnSe. A portion or theentire semiconductor layer 106 may be amorphous, polycrystalline, ormonocrystalline.

The active section 108 of the semiconductor layer 106 may function as anelectrical pathway for current flow. Although not shown in theaccompanying drawings, the active section 108 may include doped regions.Electrical contacts (not shown) may be formed above doped regions toprovide electrical interconnections to other device components in an IC.

The semiconductor detector 126 may include germanium containingcompounds and may have a thickness in the range of about 150 nm to about1000 nm. In some embodiments, the germanium containing compound isgermanium only or SiGe. As shown in FIGS. 1A to 1E, the semiconductordetector 126 is disposed in a recessed portion 134 of the active section108 of the semiconductor layer 106. Alternatively, as shown in FIG. 1F,there is no recessed portion in the active section 108 and thesemiconductor detector 126 is disposed on a planar top surface of theactive section 108 of the semiconductor layer 106. Although not shown inthe accompanying drawings, the semiconductor detector 126 may includedoped regions and may function as an electrical pathway for current flowduring operation of the device.

The waveguide section 110 of the semiconductor layer 106 functions as anoptical waveguide for the propagation of electromagnetic waves (e.g.,light waves) into the adjoining active section 108 of the semiconductorlayer 106. The active section 108 is also optically coupled to thesemiconductor detector 126, where the electromagnetic waves propagatefrom the underlying active section 108 to the overlying semiconductordetector 126 (i.e., an “evanescent coupling”).

The waveguide structure 122 is adjacent to the semiconductor detector126. In embodiments of the present disclosure, the semiconductordetector 126 has a front facet 142 facing an end facet 136 of thewaveguide structure 122. The waveguide structure 122 includes either asemiconductor material or a dielectric material.

Examples of the semiconductor material in the waveguide structure 122may include, but limited to, amorphous silicon, polycrystalline silicon,amorphous germanium, polycrystalline germanium, amorphous SiGe, orpolycrystalline SiGe. Examples of the dielectric material in thewaveguide structure 122 may include, but not limited to, silicon nitride(SiN), silicon oxynitride (SiON), aluminum nitride (AlN) or othernitride-containing compounds. In an embodiment, the waveguide structure122 preferably includes a nitride-containing compound, in particular,silicon nitride.

The waveguide structure 122 may have width and thickness dimensions(i.e., boundary conditions) that are designed for confining a particularelectromagnetic field pattern mode (for example, a transverse-magneticmode) of the propagating electromagnetic waves within the waveguidestructure 122. In particular, the thickness of the waveguide structure122 may be determined based on the geometries and dimensions of thewaveguide section 110 of the underlying semiconductor layer 106 as wellas the semiconductor detector 126. The determination of the thickness ofthe waveguide structure 122 may control the optical coupling between thewaveguide section 110 of the semiconductor layer 106 and thesemiconductor detector 126. In some embodiments, the thickness of thewaveguide structure 122 may be in a preferred range of about 100 nm toabout 500 nm.

The dielectric layer 114 has a preferred thickness in the range of about10 nm to about 76 nm. The dielectric layer 114 has a preferredrefractive index in the range of about 1.7 to about 2.2. The dielectriclayer 114 may include a dielectric material, such as silicon nitride,silicon oxynitride, or aluminum nitride. Advantageously, the dielectriclayer 114 functions as a passivation layer to provide protection for thesemiconductor detector 126 against chemical damage. More advantageously,the range of refractive indices for the dielectric layer 114 is found toenhance the optical coupling between the waveguide structure 122 and thesemiconductor detector 126, for example, by confining theelectromagnetic field pattern within the waveguide structures.

A dielectric liner 112 may be disposed on the semiconductor detector 126and between the semiconductor detector 126 and the dielectric layer 114.The dielectric liner 112 may serve as an additional protective liner forthe semiconductor detector 126 and has a thickness in the range of about5 nm to about 30 nm. The dielectric liner 112 may include anoxide-containing dielectric material such as silicon dioxide, germaniumoxide, SiGe oxide, silicon oxynitride (SiON), hafnium oxide (HfO₂),aluminum oxide (Al₂O₃), or zinc oxide (ZnO). The SiGe oxide has achemical formula of Si_((1-x))Ge_(x)O_(y), where x and y are instoichiometric ratio. In some embodiments, the dielectric liner 112 hasa refractive index in the range of about 1.4 to about 2, and preferablyabout 1.4 to about 1.7.

As shown in FIGS. 1A, 1B, 1C, 1D, and 1F, the dielectric layer 114 andthe dielectric liner 112 is between and separates the end facet 136 ofthe waveguide structure 122 and the front facet 142 of the semiconductordetector 126.

Alternatively, as shown in FIG. 1E, only the dielectric liner 112 isbetween the end facet 136 of the waveguide structure 122 and the frontfacet 142 of the semiconductor detector 126. Additionally, in FIG. 1E,the dielectric layer 114 is disposed over and covering both thesemiconductor detector 126 and the waveguide structure 122.

In the embodiments shown in FIGS. 1A, 1C, 1E and 1F, the dielectriclayer 114 and the dielectric liner 112 extend above the waveguidesection 110 of the semiconductor layer 106. In the embodiment shown inFIG. 1E, the dielectric liner 112 encapsulates the waveguide structure122.

Alternatively, in the embodiment shown in FIGS. 1B and 1D, thedielectric layer 114 and the dielectric liner 112 are disposed above theactive section 108 of the semiconductor layer 106 only.

Advantageously, by configuring the dielectric liner 112 in between thewaveguide section 110 of the semiconductor layer 106 and the waveguidestructure 122, it is found that such a configuration can provideincreased confinement of the optical modes, especially for thetransverse-magnetic (TM) mode.

The semiconductor devices described herein may further include acladding structure 124 disposed above and covering the waveguidestructure 122 and the dielectric layer 114. The cladding structure 124may function as an interlayer dielectric to provide electricalinsulation from other device components in an IC. The cladding structure124 may include multiple dielectric cladding layers. For example, thecladding structure 124 includes multiple layers of silicon oxide.

As shown in FIGS. 1A, 1B, and 1F, the waveguide structure 122 isembedded within the cladding structure 124. As shown in FIG. 1C, thewaveguide structure 122 is disposed directly on the dielectric layer114.

Alternatively, as shown in FIG. 1D, the waveguide structure 122 isdisposed directly on the waveguide section 110 of the semiconductorlayer 106 and the end facet 136 of the waveguide structure 122 isdirectly adjacent to the dielectric layer 114.

As noted above, FIG. 1F shows an embodiment having no recessed portionin the active section 108 and the semiconductor detector 126 is disposedon a planar top surface of the active section 108 of the semiconductorlayer 106. This modification will similarly apply to the embodimentshown in FIGS. 1B through 1E. This embodiment may offer the advantage ofremoving a processing step.

FIGS. 2A, 2A′, 2B, and 2B′ depict embodiments having a plurality ofwaveguide structures 122 a, 122 b, and 122 c that are vertically stackedabove the waveguide section 110 of the semiconductor layer 106, inaccordance with the present disclosure.

Referring to FIG. 2A, additional waveguide structures 122 b and 122 care formed above the embodiment shown in FIG. 1A. For example, a firstwaveguide structure 122 a is disposed above the waveguide section 110 ofthe semiconductor layer, a second waveguide structure 122 b is disposedabove the first waveguide structure 122 a, and a third waveguidestructure 122 c is disposed above the second waveguide structure 122 c.Additionally, the vertically stacked waveguide structures 122 a, 122 b,and 122 c are adjacent to the semiconductor detector 126. In particular,the end facets 136 of the waveguide structures 122 a, 122 b, and 122 care facing the front facet 142 of the semiconductor detector 126.

Although not shown by the illustrative figures, it should be understoodthat the configuration of placing additional waveguide structures abovethe embodiments depicted in FIGS. 1B to 1F are also contemplated withinthe scope of the present disclosure.

The vertically stacked waveguide structures 122 a, 122 b, and 122 c mayinclude semiconductor waveguide structures, dielectric waveguidestructures, or a combination thereof. Exemplary semiconductor anddielectric materials for the waveguide structures are the same as thosedescribed in FIGS. 1A to 1F. In some embodiments, the vertically stackedwaveguide structures include polycrystalline silicon waveguidestructures, silicon nitride waveguide structures, or a combinationthereof.

The waveguides structures 122 a, 122 b, and 122 c in the vertical stackmay have same or different geometries and sizes. For example, in theembodiment shown in FIG. 2A, the vertically stacked waveguide structures122 a, 122 b, and 122 c have substantially identical sizes.

FIG. 2A′ illustrates an alternative embodiment of FIG. 2A, in accordancewith the present disclosure. As shown in FIG. 2A′, the verticallystacked waveguide structures 122 a, 122 b, and 122 c preferablyincreases in size as they cascade towards the waveguide section 110 ofthe semiconductor layer 106.

It may be preferable for the additional waveguide structures to bevertically stacked. Advantageously, the vertical stacking of waveguidestructures 122 a, 122 b, and 122 c may provide a highly efficienttransmission in which the change of optical mode may be negligible andthe transmission efficiency across the waveguide structures 122 a, 122b, and 122 c and the waveguide section 110 of the semiconductor layer106 may be near unity.

Also advantageously, by increasing the size of the vertically stackedwaveguide structures 122 a, 122 b, and 122 c as they cascade towards thewaveguide section 110 of the semiconductor layer 106, it is found thatsuch a configuration provides adiabatic coupling between the waveguidestructures in the vertical stack with a short and compact footprint,high coupling efficiencies, low back reflections, low loss, and highfabrication-error tolerances.

The vertically stacked waveguide structures may be embedded in thecladding structure 124. As will be shown in subsequent drawings, thefirst 122 a, second 122 b and third 122 c waveguide structures may beseparated by cladding layers within the cladding structure 124.

As described herein, the dielectric layer 114 is disposed over thesemiconductor detector 126. The dielectric layer 114 may extend abovethe waveguide section 110 of the semiconductor layer 106, as similarlyshown in FIG. 1C. For example, in the embodiments shown in FIGS. 2A and2A′, the dielectric layer 114 extends to lie in between the waveguidesection 110 of the semiconductor layer 106 and the vertically stackedwaveguide structures 122 a, 122 b, and 122 c.

The dielectric layer 114 may also extend to lie in between a pair ofwaveguide structures in the vertical stack. For example, as shown inFIG. 2B, the dielectric layer 114 extends above the waveguide section110 of the semiconductor layer 106 and in between the first waveguidestructure 122 a and the second waveguide structure 122 b of the verticalstack. Alternatively, as shown in FIG. 2B′, the dielectric layer 114extends above the waveguide section 110 of the semiconductor layer 106and in between the second waveguide structure 122 b and the thirdwaveguide structure 122 c of the vertical stack.

Although FIGS. 2A, 2A′, 2B, and 2B′ illustrate three waveguidestructures in the vertical stack, it should understood that otherquantities of waveguides structures (such as two, four, five, six, etc.)in the vertical stack are also contemplated within the scope of thepresent disclosure.

FIGS. 3A to 3E and FIGS. 4A to 4D illustrate exemplary configurations ofthe semiconductor detector 126, the waveguide structure(s) 122, thewaveguide section 110 and the active section 108 of the semiconductorlayer 106. For clarity's sake, other device features, such as thedielectric layer, the dielectric liner, the cladding structure, thesubstrate, are not shown in FIGS. 3A to 3E and FIGS. 4A to 4D.Additionally, the waveguide structure(s) 122 is outlined as a rectanglein FIGS. 3A to 3E and FIGS. 4A to 4D so as not to obscure theillustration of the waveguide section 110 of the semiconductor layer 106underneath the waveguide structure(s) 122.

As shown in FIGS. 3A to 3E, the waveguide structure 122 is opticallycoupled to the semiconductor detector 126 by having the end facet 136 ofthe waveguide structure 122 aligned with the front facet 142 of theadjacent semiconductor detector 126. This coupling configuration of thewaveguide structure 122 and the semiconductor detector 126 may bereferred to as a “butt-end coupling”.

FIG. 3A depicts the waveguide structure 122 and the waveguide section110 of the semiconductor layer 106 having side facets (146 and 166,respectively) that are substantially parallel to each other.

In some embodiments, it is preferable for the waveguide structure 122and the waveguide section 110 of the semiconductor layer 106 to havetapered side facets. Tapered side facets are found to increase thecoupling efficiency and reduce the back reflection of the waves in thebutt-end coupling configuration as described above.

For example, as shown in FIG. 3B, the waveguide structure 122 has sidefacets 146 that taper away from each other as they meet the end facet136 of the waveguide structure 122.

FIG. 3C illustrates the waveguide section 110 of the semiconductor layer106 having side facets 166 that taper away from each other as they meetthe adjoining active section 108 of the semiconductor layer 106. Theside facets of the waveguide structure 122 remain substantially parallelto each other.

FIG. 3D illustrates another example in which both the waveguidestructure 122 and the waveguide section 110 of the semiconductor layer106 have tapered side facets (146 and 166, respectively) that areconfigured in the manner described in FIGS. 3B and 3C.

The waveguide section 110 of the semiconductor layer 106 may have awidth larger than, smaller than, or equal to a width of the waveguidestructure 122. The width of the waveguide section 110 and the width ofthe waveguide structure may be measured as the distance between theopposing side facets. For example, as illustrated in FIGS. 3A to 3D, thewaveguide section 110 has a smaller width than that of the waveguidestructure 122. Alternatively, as illustrated in FIG. 3E, the waveguidesection 110 has a larger width than that of the waveguide structure 122.

Although FIGS. 3A to 3E are plan views of the embodiment shown in FIG.1A, it should be understood that the exemplary layouts described inFIGS. 3A to 3E are contemplated as being applicable to the embodimentsof FIGS. 1B to 1F and FIG. 2A.

Referring to FIGS. 4A to 4D, the waveguide structures 122 a, 122 b, and122 c may be configured to have different sizes where the verticallystacked waveguide structures 122 a, 122 b, and 122 c increase in size asthey cascade towards the waveguide section 110 of the semiconductorlayer 106.

For example, as shown in FIG. 4A, the first waveguide structure 122 ahas the largest width (i.e., distance between opposing side facets 146a), the second waveguide structure 122 b having the medial width (i.e.,distance between opposing side facets 146 b) relative to the first 122 aand third 122 c waveguide structures, and the third waveguide structure122 c having the smallest width (i.e., distance between opposing sidefacets 146 c).

As another example, as shown in FIG. 4B, the first waveguide structure122 a has the largest length (i.e., distance between its front facet 148a and end facet 136 a), the second waveguide structure 122 b having themedial length (i.e., distance between its front facet 148 b and endfacet 136 b) relative to the first 122 a and third 122 c waveguidestructures, and the third waveguide structure 122 c having the smallestlength (i.e., distance between its front facet 148 c and end facet 136c).

FIG. 4C illustrates another example in which the first 122 a, second 122b and third 122 c waveguide structures differ from each other in termsof their respective length and width dimensions. As shown, thevertically stacked waveguide structures 122 a, 122 b, and 122 c have topsurface areas that increase as they cascade from the third waveguidestructure 122 c to the first waveguide structure 122 a.

The vertically stacked waveguide structures 122 a, 122 b, and 122 c mayalso be configured to have different geometries. In an embodiment, atleast one waveguide structure has side facets that taper away from eachother as they meet the end facets of the vertically stacked waveguidestructures. For example, as shown in FIG. 4D, the first waveguidestructure 122 a have side facets 146 a that are substantially parallelto each other while the second 122 a and third 122 c waveguidestructures have tapered side facets (146 b and 146 c, respectively).

Although FIGS. 4A to 4D are plan views of the embodiment shown in FIG.2A′, it should be understood that the exemplary layouts described inFIGS. 4A to 4D are contemplated as being applicable to the embodimentsof FIGS. 2B and 2B′.

Additionally, for simplicity, the illustrations in FIGS. 2A, 2A′, 2B,and 2B′ depict the waveguide section 110 having a larger width than thewidth of the waveguide structures 122 a, 122 b, and 122 c. However, itshould be understood that the embodiments shown in FIGS. 2A, 2A′, 2B,and 2B′ also contemplates configurations where the width of thewaveguide section 110 of the semiconductor layer 106 is smaller than, orequal to the width of the first waveguide structure 122 a.

A non-limiting description of the operation of the semiconductor deviceshall be described with reference to the accompanying drawings.Electromagnetic waves enter the waveguide section 110 of thesemiconductor layer 106 and propagate into the waveguide structure 122via the dielectric layer 114, as well as the adjoining active section108 of the semiconductor layer 106.

Within the waveguide structure 122, electromagnetic waves traverse alonga direction from the front facet 148 to the end facet 136 (e.g., alongthe horizontal axis) and towards the semiconductor detector 126. Theelectromagnetic waves exit the end facet 136 of the waveguide structure122, passes through the dielectric layer 114, and then enter the frontfacet 142 of the semiconductor detector 126. Hence, the propagation ofelectromagnetic waves are confined internally along the waveguidestructure 122 and the waveguide section 110 of the semiconductor layer106, which enhances the optical coupling to the adjacent semiconductordetector 126 for both TE and TM input modes. Additionally, with thepresence of the dielectric layer 114, it is found that the confinementof the guided mode (e.g., transverse-magnetic mode) in the waveguidestructure 122 increases.

Advantageously, by adding the waveguide structure 122 above thewaveguide section 110 of the semiconductor layer 106, it is found thatthe illumination and the intensity of electromagnetic waves incident onthe semiconductor detector 126 is increased (e.g., incident on its frontfacet 142). Together with the “evanescent coupling” of the waveguidesection 110 of the semiconductor layer 106 and the semiconductordetector 126, the present configuration also provides an improvedeffective index match between the waveguides and the semiconductordetector, which reduces energy loss and enhances coupling efficiency.

Referring to FIG. 5A, a cross-sectional view of a device structure forforming the semiconductor device of the present disclosure are shown. Ona substrate 102, there is provided a buried insulator layer 104 and asemiconductor layer 106 formed on the buried insulator layer 104.

Referring to FIG. 5B (FIG. 5B continues from the embodiment shown inFIG. 5A), the semiconductor layer 106 is patterned to form the waveguidesection 110 and the active section 108. The patterning of thesemiconductor layer 106 may be performed using conventional masking andpatterning techniques. The patterning may also form the waveguidesection 110 with tapered side facets, as described herein. As usedherein, “patterning techniques” includes deposition of material orphotoresist, patterning, exposure, development, etching, cleaning,and/or removal of the material or photoresist as required in forming adescribed pattern, structure or opening. Examples of conventionaltechniques for patterning include, but not limited to, wet etchlithographic processes, dry etch lithographic processes or directpatterning processes.

Referring to FIG. 5C (FIG. 5C continues from the embodiment shown inFIG. 5B), a semiconductor detector 126 is formed on the active section108 of the semiconductor layer 106. In some embodiments, the activesection 108 may be patterned using conventional patterning techniques toform a recessed portion 134 before forming the semiconductor detector126. Alternatively, the semiconductor detector 126 is formed on a planarsurface of the active section 108.

The formation of the semiconductor detector 126 may include the use ofepitaxial growth (such as molecular beam epitaxy (MBE), liquid phaseepitaxy, vapor phase epitaxy, or solid phase epitaxy), rapid meltgrowth, and/or deposition of a semiconductor material.

Referring to FIG. 5D, a dielectric liner 112 is formed on thesemiconductor detector 126 and the waveguide section 110 of thesemiconductor layer 106. Thereafter, a dielectric layer 114 is formed onthe dielectric liner 112. Formation of the dielectric liner 112 and thedielectric layer 114 may be performed using conventional depositiontechniques. The dielectric liner 112 may be formed during replacementmetal gate processes in conventional semiconductor fabrication forintegration with other device components in an IC (e.g., integrationwith a complementary metal oxide semiconductor (CMOS) device).

As used herein, “deposition techniques” refer to the process of applyinga material over another material (or the substrate). Exemplarytechniques for deposition include, but not limited to, spin-on coating,sputtering, chemical vapor deposition (CVD), physical vapor deposition(PVD), molecular beam deposition (MBD), pulsed laser deposition (PLD),liquid source misted chemical deposition (LSMCD), atomic layerdeposition (ALD). In some embodiments, a conformal deposition process ispreferred to deposit the dielectric liner 112 and the dielectric layer114, e.g., an ALD process or a highly-controlled CVD process.

Although not shown in the accompanying drawings, in some embodiments,the dielectric layer 114 may be formed using deposition of multipleliners. For example, the dielectric layer 114 may include a first linerhaving a thickness in the range of about 10 nm to about 60 nm and asecond liner having a thickness in the range of about 10 nm to about 16nm. The first and second liners may be of the same dielectric material.

In an embodiment (not shown), the dielectric liner 112 and thedielectric layer 114 may be patterned such that the dielectric liner 112and the dielectric layer 114 is disposed above the active section 108 ofthe semiconductor layer 106 only and the waveguide section 110 of thesemiconductor layer 106 is exposed.

Referring to FIG. 5E, a first cladding layer 124 a is formed on thedielectric layer 114, followed by forming a first waveguide structure122 a on the first cladding layer 124 a. The first cladding layer 124 amay be formed using conventional deposition techniques and may conformto the dielectric layer 114. The first waveguide structure 122 a may beformed by depositing a semiconductor material layer or a dielectricmaterial layer on the first cladding layer 124 a, followed by patterningto form front facet 148 a, end facet 136 a and side facets thereof. Asdescribed herein, the side facets of the first waveguide structure 122 amay be tapered.

In another embodiment (not shown), the first waveguide structure 122 amay be formed directly on the dielectric layer 114 and then patternedsuch that the end facet 136 a is directly adjacent to the dielectriclayer 114. Thereafter, the first cladding layer 124 a is deposited onthe first waveguide structure 122 a and the dielectric layer 114.

In yet another embodiment (not shown), the first waveguide structure 122a may be formed directly on the exposed waveguide section 106 of thesemiconductor layer 106 followed by the deposition of the first claddinglayer 124 a.

Exemplary semiconductor devices described in FIGS. 1A to 1D and 1F maybe formed at this stage of the process by depositing an additionalcladding layer to cover the first waveguide structure 122 a. Themultiple cladding layers formed during the processing stages constitutethe cladding structure 124 as described herein.

The semiconductor devices may also be subjected to further semiconductorprocessing for integration with other device components in an IC.Examples of further processing may include the formation ofback-end-of-line (BEOL) structures such as redistribution layers,interlayer dielectric isolation structure and interconnect structuresabove the cladding structure 124. The BEOL structures may also provideprotection for the semiconductor detector 126 and the waveguidestructure 122.

Referring to FIG. 5F (FIG. 5F continues from the embodiment shown inFIG. 5E), a second cladding layer 124 b is formed to cover the firstwaveguide structure 122 a. Thereafter, a second waveguide structure 122b is formed on the second cladding layer 124 b. The formation of thesecond cladding layer 124 b and the second waveguide structure 122 b maybe performed using the same deposition and patterning techniquesdescribed in FIG. 5E. An additional cladding layer may be deposited atthis stage of the process to cover the second waveguide structure 122 b,thereby forming another exemplary semiconductor device of the presentdisclosure.

Referring to FIG. 5G (FIG. 5G continues from the embodiment shown inFIG. 5F), a third cladding layer 124 c is formed to cover the secondwaveguide structure 122 b. Thereafter, a third waveguide structure 122 cis formed on the third cladding layer 124 c. The formation of the secondcladding layer 124 b and the second waveguide structure 122 b may beperformed using the same deposition and patterning techniques describedin FIG. 4E. The thicknesses of each waveguide structure 122 a, 122 b,and 122 c may be controlled by the deposition process to form the same.

Exemplary semiconductor devices described in FIGS. 2A and 2A′ may beformed at this stage of the process by depositing an additional claddinglayer to cover the third waveguide structure 122 c. The multiplecladding layers formed during the processing stages constitute thecladding structure 124 as described herein. Depending on the designrequirements of the semiconductor devices, additional waveguidestructures may be included in the device configuration by repeating thesteps described in FIGS. 5E to 5G.

The semiconductor devices may also be subjected to further semiconductorprocessing for integration with other device components in an IC.Examples of further processing may include formation of back-end-of-line(BEOL) structures such as redistribution layers, interlayer dielectricisolation structures and interconnect structures above the claddingstructure 124. The BEOL structures may also provide protection for thesemiconductor detector 126 and the waveguide structures 122 a, 122 b,and 122 c.

FIGS. 5D′ to 5G′ illustrate another exemplary process for forming thesemiconductor device of the present disclosure. Referring to FIG. 5D′(FIG. 5D′ continues from the embodiment shown in FIG. 5C), thedielectric liner 112 is formed on the semiconductor detector 126, theactive section 108 and the waveguide section 110 of the semiconductorlayer 106 using conventional deposition techniques. For example, thedielectric liner 112 is formed using a conformal deposition process,e.g., an ALD process or a highly-controlled CVD process. Thereafter, afirst waveguide structure 122 a is formed on the dielectric liner 112using the same techniques as described in FIG. 5E.

Referring to FIG. 5E′ (FIG. 5E′ continues from the embodiment shown inFIG. 5D′), additional deposition of the dielectric liner 112 isperformed to encapsulate the first waveguide structure 122 a.Thereafter, a dielectric layer 114 is formed on the dielectric liner 112using conventional deposition techniques. Additional deposition ofcladding layers may be performed to form the exemplary semiconductordevice shown in FIG. 1E.

Referring to FIGS. 5F′ and 5G′ (FIG. 5F′ continues from the embodimentshown in FIG. 5E′, and FIG. 5G′ continues from the embodiment shown inFIG. 5F′), a plurality of waveguide structures vertically stacked abovethe waveguide section 110 of the semiconductor layer 106 is formed usingthe same techniques described in FIGS. 5F and 5G.

For example, as shown in FIG. 5F′, a first cladding layer 124 a isdeposited on the dielectric layer 114 followed by the deposition of asecond waveguide structure 122 b. An additional cladding layer may bedeposited to cover the second waveguide structure 122 b at this stage ofthe process to form another exemplary semiconductor device of thepresent disclosure.

As shown in FIG. 5G′, a second cladding layer 124 b is deposited tocover the second waveguide structure 122 b followed by the deposition ofa third waveguide structure 122 c. An additional cladding layer may bedeposited to cover the embodiment shown in FIG. 5G′ to form theexemplary semiconductor device shown in FIG. 2B.

Alternatively, although not shown in the accompanying drawings, theembodiment shown in FIG. 2B′ may be formed by performing additionaldeposition of the dielectric liner 112 to encapsulate the first 122 aand second 122 b waveguide structures, the deposition of the dielectriclayer 114 on the dielectric liner 112, and the formation of the thirdwaveguide structure 122 c and the cladding layers above the dielectriclayer 114 thereafter.

The embodiment shown in FIG. 5G′ may also be subjected to furthersemiconductor processing for integration with other device components inan IC. Examples of further processing may include formation ofback-end-of-line (BEOL) structures such as redistribution layers,interlayer dielectric isolation structures and interconnect structuresabove the cladding structure 124.

Referring to FIG. 6, an example of a semiconductor comparative testdevice without a waveguide structure is shown. As shown, thesemiconductor device has a substrate 102, a buried insulator layer 104on the substrate 102, a semiconductor layer 106 on the buried insulatorlayer 104 and having a waveguide section 110 and an adjoining activesection 108, a semiconductor detector 126 disposed on the active section108, and a cladding structure 124 disposed on the semiconductor layer106 and the semiconductor detector 126. The comparative test device alsodoes not have a dielectric liner 112 and a dielectric layer 114.

A computer simulation study was conducted to compare the couplingefficiencies of the embodiments shown in FIG. 1A and FIG. 2A againstthat of the comparative test device shown in FIG. 6. The simulation wasperformed using software by Lumerical. The exemplary configurations ofthe semiconductor device were modelled using a Finite-differencetime-domain (FDTD) method and the transmission of electromagnetic waveswas simulated in both transverse-electric (TE) and transverse-magnetic(TM) modes.

For the purposes of the simulation study, the substrate 102 wassimulated as a silicon substrate having a buried silicon dioxide layer104. The semiconductor detector 126 was simulated as a germaniumdetector, the semiconductor layer 106 was simulated as a monocrystallinesilicon layer, and the cladding structure 124 was simulated usingsilicon dioxide material.

Additionally, for the embodiments illustrated in FIG. 1A and FIG. 2A,the dielectric liner 112 was simulated as a silicon dioxide liner andthe dielectric layer 114 was simulated as a silicon nitride layer. ForFIG. 1A, the waveguide structure 122 was simulated using silicon nitridewhereas for FIG. 2A, the vertically stacked waveguide structures 122 a,122 b, and 122 c were simulated using polycrystalline silicon. For bothof the embodiments illustrated in FIG. 1A and FIG. 2A, the waveguidestructures 122 had identical dimensions (e.g., thickness, length andwidth).

Based on the simulation study, the comparative example was found to havea modal effective index of 1.82 and a coupling efficiency of 66%. Incontrast, the simulated embodiment using FIG. 1A was found to have amodal effective index of 2.02 and a coupling efficiency of 79%, whilethe simulated embodiment using FIG. 2A was found to have a modaleffective index of 2.45 and a coupling efficiency of 93%.

Advantageously, it was found that the simulated embodiments of FIG. 1Aand FIG. 2A had coupling efficiencies and modal effective indices thatare higher than that of the comparative example of FIG. 6, and thereforeprovided improved modal overlap and increase confinement of thefundamental and/or higher-order TE and TM modes.

It should be noted that in addition to the fundamental modes used in thesimulation study, higher-order modes may be excited by the inputwaveguides as well, depending on the geometries and dimensions of thedevice components. The improvement in the overall coupling efficiencymay lead to enhanced performance of the semiconductor detector (e.g., aphotodetector). For instance, the responsivity may be significantlyimproved owing to the optimized optical coupling and light absorption.

Throughout this disclosure, the terms top, upper, upwards, over, andabove refer to the direction away from the substrate. Likewise, theterms bottom, lower, downwards, under, and below refer to the directiontowards the substrate. It is to be understood that the terms so used areinterchangeable under appropriate circumstances such that theembodiments of the device described herein are, for example, capable ofoperation in other orientations than those illustrated or otherwisedescribed herein.

Similarly, if a method is described herein as involving a series ofsteps, the order of such steps as presented herein is not necessarilythe only order in which such steps may be performed, and certain of thestated steps may possibly be omitted and/or certain other steps notdescribed herein may possibly be added to the method. Furthermore, theterms “comprise”, “include”, “have”, and any variations thereof, areintended to cover a non-exclusive inclusion, such that a process,method, article, or device that comprises a list of elements is notnecessarily limited to those elements, but may include other elementsnot expressly listed or inherent to such process, method, article, ordevice. Occurrences of the phrase “in an embodiment” herein do notnecessarily all refer to the same embodiment.

The descriptions of the various embodiments of the present disclosurehave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein. Furthermore, there is no intention to be bound by anytheory presented in the preceding background or the following detaileddescription.

Additionally, the various tasks and processes described herein may beincorporated into a more comprehensive procedure or process havingadditional functionality not described in detail herein. In particular,various processes in the manufacture of integrated circuits arewell-known and so, in the interest of brevity, many conventionalprocesses are only mentioned briefly herein or omitted entirely withoutproviding the well-known process details.

As will be readily apparent to those skilled in the art upon a completereading of the present application, the semiconductor devices andmethods disclosed herein may be employed in manufacturing a variety ofdifferent integrated circuit products and modules, including, but notlimited to, CMOS devices, optoelectronic modules, LIDAR instrumentationand LIDAR systems, etc.

What is claimed is:
 1. A semiconductor device comprising: a substrate; asemiconductor layer having a waveguide section and an adjoining activesection above the substrate; a semiconductor detector disposed on theactive section of the semiconductor layer, the semiconductor detectorhaving a front facet; a dielectric layer disposed over the semiconductordetector; and a waveguide structure above the waveguide section of thesemiconductor layer and adjacent to the semiconductor detector, thewaveguide structure having an end facet that faces the front facet ofthe semiconductor detector; wherein the dielectric layer is between theend facet of the waveguide structure and the front facet of thesemiconductor detector.
 2. The device of claim 1, further comprising thedielectric layer extending between the waveguide section of thesemiconductor layer and the waveguide structure.
 3. The device of claim1, further comprising the waveguide structure having side facets thattaper away from each other as they meet the end facet of the waveguidestructure.
 4. The device of claim 1, further comprising the waveguidesection of the semiconductor layer has side facets that taper away fromeach other as they meet the active section of the semiconductor layer.5. The device of claim 1, wherein the waveguide structure is asemiconductor material or a dielectric material.
 6. The device of claim1, wherein the waveguide structure is a first waveguide structure andfurther comprising a second waveguide structure vertically stacked abovethe first waveguide structure.
 7. The device of claim 1, furthercomprising a cladding structure disposed above the waveguide structureand the dielectric layer.
 8. A semiconductor device comprising: asubstrate; a semiconductor layer having a waveguide section and anadjoining active section above the substrate; a semiconductor detectordisposed on the active section of the semiconductor layer; a dielectriclayer disposed over the semiconductor detector; and a plurality ofwaveguide structures that are vertically stacked above the waveguidesection of the semiconductor layer and adjacent to the semiconductordetector, wherein the dielectric layer extends above the waveguidesection of the semiconductor layer and in between a pair of waveguidestructures in the vertical stack.
 9. The device of claim 8, wherein thevertically stacked waveguide structures further comprising semiconductorwaveguide structures or dielectric waveguide structures, or acombination thereof.
 10. The device of claim 8, wherein the verticallystacked waveguide structures increase in size as they cascade towardsthe waveguide section of the semiconductor layer.
 11. The device ofclaim 8, wherein the semiconductor detector has a front facet that isfacing end facets of the vertically stacked waveguide structures. 12.The device of claim 11, wherein the plurality of vertically stackedwaveguide structures further comprising at least one waveguide structurehaving side facets that taper away from each other as they meet the endfacets of the vertically stacked waveguide structures.
 13. The device ofclaim 8, wherein the vertically stacked waveguide structures havesubstantially identical sizes.
 14. The device of claim 7, wherein thewaveguide structure is embedded within the cladding structure.
 15. Thedevice of claim 1, further comprising a dielectric liner disposed on thesemiconductor detector and the dielectric layer being disposed on thedielectric liner, wherein the dielectric liner is between the end facetof the waveguide structure and the front facet of the semiconductordetector.
 16. The device of claim 15, wherein the dielectric liner andthe dielectric layer extend between the waveguide section of thesemiconductor layer and the waveguide structure.
 17. A semiconductordevice comprising: a substrate; a semiconductor layer having a waveguidesection and an adjoining active section above the substrate; asemiconductor detector disposed on the active section of thesemiconductor layer; a dielectric layer disposed over the semiconductordetector; and a plurality of waveguide structures that are verticallystacked above the waveguide section of the semiconductor layer andadjacent to the semiconductor detector, wherein the dielectric layerextends to lie between the waveguide section of the semiconductor layerand the vertically stacked waveguide structures.
 18. The device of claim17, further comprising a cladding structure disposed above thedielectric layer, wherein the vertically stacked waveguide structuresare embedded in the cladding structure and each waveguide structure isseparated by cladding layers within the cladding structure.
 19. Thedevice of claim 18, wherein the vertically stacked waveguide structuresincrease in size as they cascade towards the waveguide section of thesemiconductor layer.
 20. The device of claim 19, wherein thesemiconductor detector has a front facet that is facing end facets ofthe vertically stacked waveguide structures, and the plurality ofvertically stacked waveguide structures further comprising at least onewaveguide structure having side facets that taper away from each otheras they meet the end facets of the vertically stacked waveguidestructures.